That's a very interesting question. We could ask some Messenger and Instagram people, since they are heavily using BuckleScript. In general output JS is already

That's a very interesting question. We could ask some Messenger and Instagram people, since they are heavily using BuckleScript. In general output JS is already fairly spartan, because BuckleScript uses a few tricks here and there, like encoding modules and records as arrays instead of objects; and completely inlining functions whenever it can. BuckleScript also emits ES6 modules, with imports and exports, and it marks its output as either pure or impure at the module level. So potentially there's a lot of room for bundlers to do tree-shaking. Bob Zhang, the BuckleScript team lead, is working on a new typesafe standard library for BuckleScript, which takes advantage of compile-time checks to compile to extremely minimal and idiomatic JS. Exciting times up ahead!